DESCRIPTION: The objective of this application is to develop a comprehensive understanding of the role of cellular fibronectin (cFN) in hepatic stellate cell (HSC) function and liver fibrosis. Cellular fibronectin (cFN) can contain two alternatively spliced domains, termed extra domain A (EDA) and B (EDB), which are not expressed in the normal liver but are markedly upregulated during liver fibrosis, where they may activate specific integrins and thereby specific cells including HSC, the predominant fibrogenic cells in liver fibrosis. We hypothesize that HSC interaction with cFN triggers unique integrin signaling pathways and that cFN plays a causative role in liver fibrosis by enhancing HSC myofibroblastic differentiation, fibrogenesis and motility. Aim 1: To determine the mechanism by which HSC interact with cFN and to define the effect of this interaction on HSC motility. Interactions between the EDA and EDB domains of cFN and integrin receptors on HSC will be identified using integrin binding assays. The significance of these interactions will be determined by measuring flux through integrin signaling pathways, and their effect on HSC motility will be examined using transwell assays and scratch tests. Aim 2: To determine the requirement for cFN in HSC myofibroblastic differentiation and liver fibrosis. In vitro, the role of cFN in HSC differentiation will be characterized by measuring HSC contractility, ECM deposition, and expression of myofibroblast markers. In vivo, the extent of liver fibrosis and HSC myofibroblastic differentiation will be measured following bile duct ligation or carbon tetrachloride administration in wild type or EDA-/- mice. All forms of chronic liver injury lead to the final common outcome of liver fibrosis, which often progresses to cirrhosis. Chronic liver injury and cirrhosis represent a significant source of morbidity and mortality in the United States, and liver transplant remains the only therapeutic option for end stage liver disease. Thus, there is a need for greater understanding of the molecular events that underlie fibrosis. This proposal will attempt to illuminate one such event by defining the role of cellular fibronectin in liver fibrosis.